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private val prominentThreshold = context.resources.getDimensionPixelSize(R.dimen.prominent_threshold)

// In scaleChildren:
for (i in 0 until childCount) {
    val distanceToCenter = ...
    child.isActivated = distanceToCenter < prominentThreshold
}

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class OverlayableImageView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : ConstraintLayout(context, attrs, defStyleAttr) {

    private val imageView: ImageView
    private val sendButton: ImageButton

    init {

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vh.imageView.setOnClickListener {
    val rv = vh.imageView.parent as RecyclerView
    rv.smoothScrollToCenteredPosition(position)
}

fun RecyclerView.smoothScrollToCenteredPosition(position: Int) {
    val smoothScroller = object : LinearSmoothScroller(context) {

        override fun calculateDxToMakeVisible(view: View?,
                                              snapPref: Int): Int {

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var translationXForward = 0f

for (i in 0 until childCount) {
    val translationXFromScale = ... // like before
    child.translationX = translationXForward + translationXFromScale

    translationXForward = 0f

    if (translationXFromScale > 0 && i >= 1) {
        // Edit previous child

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val translationDirection = if (childCenter > containerCenter) -1 else 1
val translationXFromScale = translationDirection * child.width * (1 - scale) / 2f
child.translationX = translationXFromScale

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internal class ProminentLayoutManager(
    context: Context,
    private val minScaleDistanceFactor: Float = 1.5f,
    private val scaleDownBy: Float = 0.5f
) : LinearLayoutManager(context, HORIZONTAL, false) {

    override fun onLayoutCompleted(state: RecyclerView.State?) =
        super.onLayoutCompleted(state).also { scaleChildren() }

    override fun scrollHorizontallyBy(

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private fun initRecyclerViewPosition(position: Int) {
    // This initial scroll will be slightly off because it doesn't
    // respect the SnapHelper. Do it anyway so that the target view
    // is laid out, then adjust onPreDraw.

    layoutManager.scrollToPosition(position)

    recyclerView.doOnPreDraw {
        val targetView = layoutManager.findViewByPosition(position)
                ?: return@doOnPreDraw

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class BoundsOffsetDecoration : ItemDecoration() {
    override fun getItemOffsets(outRect: Rect,
                                view: View,
                                parent: RecyclerView,
                                state: RecyclerView.State) {
        super.getItemOffsets(outRect, view, parent, state)

        val itemPosition = parent.getChildAdapterPosition(view)

        // It is crucial to refer to layoutParams.width

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override fun onBindViewHolder(vh: VH, position: Int) {
    val image = images[position]

    // Resize view to respect aspect ratio
    val imageAspectRatio = image.aspectRatio

    val targetImageWidth: Int =
        if (imageAspectRatio < maxImageAspectRatio) {
            // Tall image: height = max, width adjusts
            (maxImageHeight * imageAspectRatio).roundToInt()

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private var hasInitParentDimensions = false
private var maxImageWidth: Int = 0
private var maxImageHeight: Int = 0
private var maxImageAspectRatio: Float = 1f

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH {
    if (!hasInitParentDimensions) {
        maxImageWidth = parent.width
        maxImageHeight = parent.height
        maxImageAspectRatio = maxImageWidth.toFloat() / maxImageHeight.toFloat()